linux-kernel - Re: [RFC PATCH 00/17] Drop uses of pci_read_config

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Date:   Sun, 2 Aug 2020 19:28:00 +0200
From:   Saheed Bolarinwa <refactormyself@...il.com>
To:     Borislav Petkov <bp@...en8.de>, trix@...hat.com
Cc:     helgaas@...nel.org, Kalle Valo <kvalo@...eaurora.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Wolfgang Grandegger <wg@...ndegger.com>,
        Marc Kleine-Budde <mkl@...gutronix.de>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Richard Weinberger <richard@....at>,
        Vignesh Raghavendra <vigneshr@...com>,
        Joerg Roedel <joro@...tes.org>, bjorn@...gaas.com,
        skhan@...uxfoundation.org,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        linux-mtd@...ts.infradead.org, iommu@...ts.linux-foundation.org,
        linux-rdma@...r.kernel.org, linux-ide@...r.kernel.org,
        linux-i2c@...r.kernel.org, linux-hwmon@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, intel-gfx@...ts.freedesktop.org,
        linux-gpio@...r.kernel.org, linux-fpga@...r.kernel.org,
        linux-edac@...r.kernel.org, dmaengine@...r.kernel.org,
        linux-crypto@...r.kernel.org,
        linux-atm-general@...ts.sourceforge.net
Subject: Re: [RFC PATCH 00/17] Drop uses of pci_read_config_*() return value


On 8/1/20 2:56 PM, Borislav Petkov wrote:
> On Sat, Aug 01, 2020 at 01:24:29PM +0200, Saheed O. Bolarinwa wrote:
>> The return value of pci_read_config_*() may not indicate a device error.
>> However, the value read by these functions is more likely to indicate
>> this kind of error. This presents two overlapping ways of reporting
>> errors and complicates error checking.
> So why isn't the *value check done in the pci_read_config_* functions
> instead of touching gazillion callers?
Because the value ~0 has a meaning to some drivers and only
drivers have this knowledge. For those cases more checks will
be needed to ensure that it is an error that has actually
happened.
> For example, pci_conf{1,2}_read() could check whether the u32 *value it
> just read depending on the access method, whether that value is ~0 and
> return proper PCIBIOS_ error in that case.

The primary goal is to make pci_config_read*() return void, so
that there is *only* one way to check for error i.e. through the
obtained value.
Again, only the drivers can determine if ~0 is a valid value. This
information is not available inside pci_config_read*().

- Saheed